[Spa] Gradle and Android Gradle Plugin Upgrade

Gradle: Upgraded from version 8.12.1 to 8.13
Android Gradle Plugin (AGP): Upgraded from version 8.10.1 to 8.11.0

Build Script Modernization and Centralization:
The root `build.gradle.kts` file has been substantially refactored to
use the modern, stable AGP APIs and to centralize configuration.
Modern AGP APIs: The build script now uses the
`com.android.build.api.dsl` interfaces (`CommonExtension`,
`ApplicationExtension`, `LibraryExtension`) instead of the older
`com.android.build.gradle.BaseExtension`. This is the recommended
practice for modern AGP versions, providing more stable and explicit
APIs.

Bug: 373245944
Flag: EXEMPT gradle only
Test: gradle build
Change-Id: I3b1688753f7859ee3e58ddd7066730f7dae85967